Transient voltage spikes and voltage pulses in electronic circuits can be caused by an electrostatic discharge (ESD) event. Such ESD events can occur when two charged objects are brought into close physical proximity and are the result of an imbalance of electric potential between the two objects. A common example of an ESD event is the release of static electricity by a person touching, for example, a metal doorknob. Transient voltage spikes and pulses frequently exceed the safe operating margin of sensitive electronic components, semiconductor devices, discrete circuits, and integrated circuits (ICs) causing permanent damage. Large ESD events may render the affected component inoperable whereas repeated smaller ESD events can cause damage over time leading to reliability issues and eventual inoperability.
ESD protection circuits may be implemented as discrete circuits, but many ICs include integrated ESD protection circuits designed to protect the IC from ESD events and other transient voltage events. Typical ESD protection circuits ensure a low impedance path that does not include the protected circuit in the event that an unsafe voltage value is met or exceeded. This can be accomplished through incorporation of passive or active circuit elements. Active clamp ESD protection circuits are designed to turn on when a trigger condition is met or exceeded. Such ESD protection circuits utilize trigger circuits to control active circuit elements such as transistors. In the event that a designed trigger voltage VTR is met or exceeded, the active circuit element acts as a discharge element providing an alternate path for the majority of the overvoltage current instead of passing through the protected circuit. Active clamp ESD protection circuits that are designed to operate in high voltage applications are referred to as high voltage active clamp (HVAC) circuits.
ESD protection circuits are often fabricated on bulk silicon technologies in order to maintain low costs. Bulk silicon technologies are commonly used for producing semiconductor components.